Homeostasis and Transport

Question 1

How can ions/molecules be transported across cell membranes?

Answer 1

Movement of ions through channels into cells; pumping of ions/molecules against a concentration gradient (ATP always required against concentration gradient)

Question 2

Three examples of passive transport?

Answer 2

diffusion, osmosis, facilitated diffusion

Question 3

Two examples of active transport?

Answer 3

pumps and cotransporters

Question 4

What are four factors that affect diffusion rate?

Answer 4

membrane permeability (how open channels are), concentration difference, electronegative potential across membrane, pressure (blood capillaries)

Question 5

What is the extracellular concentration of Na+? Intracellular?

Answer 5

140 mM, 10mM

Question 6

What is the extracellular concentration of K+? Intracellular?

Answer 6

4mM, 140mM

Question 7

What is the extracellular concentration of Ca++? Intracellular?

Answer 7

2.4mM, 0.0001mM

Question 8

What is the extracellular concentration of Cl-? Intracellular?

Answer 8

103mM, 4mM

Question 9

Aquaporin is a transmembrane protein that increases the passive movement of what molecule across the plasma membrane?

Answer 9

Water, simple diffusion

Question 10

What is an example of facilitated diffusion? What does it require, and how would you explain it?

Answer 10

Glucose transport inside pancreatic cells, it requires a carrier protein but does not require ATP to enter the cell (facilitated diffusion) because it is going down its concentration gradient

Question 11

What is an example of a voltage gated channel that uses simple diffusion?

Answer 11

voltage gated Na+ channel in neurons

Question 12

What is an example of a chemically gated channel?

Answer 12

Ach nicotinic receptors that require a conformational change when Ach binds, causes the cellular response

Question 13

Resting membrane potential in neurons?

Answer 13

-70mV

maintained using selective permeability of ions and Na+/K+ ATPase

Question 14

How is an action potential generated?

Answer 14

A. Depolarization to Threshold: Signaled by the brain, sodium leaks slowly until it reaches threshold ->When -60 miliwats (the threshold) is reached, action potential occurs

B. Activation of Sodium Channels and Rapid Depolarization: Sodium channels open ->Positive sodium ions rush in; Depolarization: Membrane potential moves positive; More sodium ions
Cells have different depolarization rates

C. Inactivation of Sodium Ions and Activation of Potassium Ions: Sodium channel closes ->Potassium channel opens ->Positive potassium ions rush in
Hyperpolarization (also known as Repolarization): Membrane potential moves negative; More potassium ions; While repolarizing, the levels go below the proper resting state of -70 miliwats ? In order to go into a resting state, it much be exactly -70 milliwatts

D. Both Channels are Closed -> Goes to a Resting State: Resting state is negative ->Refractory Period: When action potential occurs until resting state

Question 15

What is vmax when related to facilitated diffusion?

Answer 15

Determined by concentration of carrier molecules & rate of movement of carrier molecules across channel. Simple diffusion has no vmax.

Question 16

What is active transport?

Answer 16

The movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy.

Question 17

What are examples of primary active transport?

Answer 17

Na+/K+ ATPase, Ca++ ATPase, H+ pump

Requires energy in the form of ATP

Question 18

What is secondary active transport? What are the two types?

Answer 18

Uses energy of one solute moving with the concentration gradient (created previously with primary active transport) to move another substance against the concentration gradient

1. Cotransporters (symporters)- both ions in the same direction (one ‘uphill’ and one ‘downhill’)
2. Exchangers (counter-transport)- antiport- ions move in separate directions (one ‘uphill’ and one ‘downhill’)

Question 19

What are some examples of cotransporters?

Answer 19

Na/Glucose transporter Couples the Na+ gradient to move another molecule against its gradient). Na also transports amino acids and phosphate against their gradients.

Question 20

What are some examples of exchangers?

Answer 20

Na/Ca exchanger, and the Na/H exchanger. Na moves into the cell bringing calcium and hydrogen out of the cell (against their gradient)

Question 21

What is osmosis?

Answer 21

Solvent moving from area of high solvent concentration to low solvent concentration across semipermeable membrane

Question 22

What is osmotic pressure?

Answer 22

Pressure required to maintain an equilibrium with no net movement of solvent

Question 23

What is osmolarity?

Answer 23

osmoles of solute (can dissociate within solution) per liter of solution.
1 mole of NaCl yields 2 osmoles of solute particles in water

Question 24

What happens if a cell is placed in a hypertonic solution?

Answer 24

Will cause water to rush out of a cell.
In many cases the solution (usually water) has a greater solute concentration (hyperosmotic) compared to the inside of a cell and where the solutes don’t easily/quickly equilibrate between solutions

Question 25

What happens if a cell is placed in a hypotonic solution?

Answer 25

Will cause water to rush into the cell.
In many cases, the solution has a lesser solute concentration (hypoosmotic) compared to the inside of a cell and where the solutes don’t easily/quickly equilibrate between solutions

Question 26

What happens if a cell is placed in a isotonic solution?

Answer 26

Nothing. Has the same solute concentration compared to the inside of a cell.